Sintered alloy and method of manufacturing the same

ABSTRACT

A sintered alloy that enables the reducing of coefficient of friction and the sealing of pores on a surface thereof and a method of manufacturing the same. A sintered alloy body includes a resin film layer and pores. The pores define a porosity ranging from 2 to 35 volume %, each having an inlet portion and an inside portion, defining a pore inlet diameter and a pore inside diameter respectively. The pore inlet diameter ranges from 10 to 200 μm, and an average ratio of the pore inlet diameter to the pore inside diameter is at least. Solid lubricant is dispersed in the resin film layer. After forming the layer  3 , it is pressed against the sintered alloy body. Thus, the layer enters into the pores to closely contact them, thereby sealing the pores, reducing the coefficient of friction due to the solid lubricant.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a sintered alloy and a method ofmanufacturing the same.

[0003] 2. Description of the Related Art

[0004] A porous body is produced for example by sintering metallic orceramic materials, or by adhesion-bonding of material powders, any ofwhich causes resultant pores on a surface of the porous body so thatfriction resistance becomes large.

[0005] Sintered alloys produced by sintering metallic powders areadvantageous not only in that they have stable qualities and are suitedto mass production, but also in that they enable the use of certainmaterials of which the composition is very unlikely to be employed ifsoluble materials are chosen, and thus they have been used for themanufacture of various kinds of members in the past.

[0006] Conventionally, boron nitride or fluoroplastic materials withexcellent lubrication properties have been mixed in the material powdersin the case that slidability relative to other members is required, sothat a sliding surface with less friction resistance has been formed, asdisclosed in Japanese Un-Examined Patent Publication Nos. 10-280083 and11-50103.

[0007] According to such conventional structure that fluoroplasticmaterials or the like are contained in material powers, however, poresremain exposed to the external surface even if lubrication property isimproved to an certain extent, and thus surface treatment has beennecessary in order to improve air-tightness.

[0008] On the other hand, sintered alloys have a lot of advantages asabove mentioned, such as stable qualities, mass-production-suitedproperties, enabling the use of materials whose composition is unlikelyto be realized if soluble materials are used, as well as the enabling ofthe manufacture of porous bodies. By taking advantage of theseadvantages, different types of sintered products suitable for specificbearings have been widely used in the past, such as those which can savemuch of lubricant-supplying trouble and are able to be disposed in aplace where lubrication is difficult.

[0009] In the manufacture of such sintered bearings, material powercontaining metal powder as a main component is subjected to compactingto form a green compact, using a powder compacting device, and then thegreen compact thus formed is sintered in a sintering furnace to form asintered body, which may undergo a sizing process if necessary.

[0010] Whereas, relative thrust movement between a bearing and a shaftis generally regulated by a snap ring fixed to the shaft. Between thesnap ring and the bearing are disposed a plurality of washers made ofrubber or resin such as polyacetal, in order to prevent the abrasion ofthe snap ring or the oil leakage from a bearing edge of an oil-retainingbearing.

[0011] However, washers in direct contact with the bearing are rotatedtogether with the rotation of the snap ring associated by the rotationof the shaft, and thus they are rubbed against the edge of the bearingand eventually worn away. While this problem occurs in the case of thebearings made of soluble metal as well, porous bearings have such porousfront surfaces (particularly end faces) that washers are apt to besubjected to abrasion, which is further facilitated due to the increaseof friction when a thrust load is applied to the shaft.

[0012] Further, if abrasion material of the washers produced by thesliding between the washers and the bearing enters between the shaft andthe bearing, the oil exudation from the oil-retaining bearing ishindered, while lubrication material on a surface of “dry bearing”(oilless bearing) is covered with such abrasion powder, and thus thereis a problem that burning or abrasion wear of the shaft is likely tooccur. For oil-retaining bearings, even if washers are disposed on theend faces thereof, such washers do not suffice to prevent the oilleakage from the end faces thereof, thus leading to a risk of shortageof lubricant or contamination of peripheral components.

[0013] To solve the problem, the end faces of the bearings haveheretofore been subjected to lathe cutting process or burnishing processso as to be smoothed and sealed, in order to prevent the abrasion of thewashers and the lubricant leakage from the end faces of the bearings.However, the conventional method has had drawbacks that not onlymanufacturing time and costs increase due to the increase of machineworks, but it has been difficult to prevent the abrasion of the washersdue to the mutual sliding between the washers and the bearings evenafter such mechanical works.

SUMMARY OF THE INVENTION

[0014] In view of the above problems, it is, therefore, an object of thepresent invention to provide a sintered alloy with reduced coefficientof friction and sealed pores on a surface as well as a method ofmanufacturing the same.

[0015] It is another object of the present invention to provide asintered alloy which prevents of the abrasion of resinous washers rubbedagainst a bearing body made of such sintered alloy and the lubricantleakage from an end face of the bearing, as well as a method ofmanufacturing the same.

[0016] To attain the objects, there is proposed a sintered alloyaccording to a first aspect of the invention, including a sintered alloybody which is formed by compacting material powders and then sinteringthe same,

[0017] wherein the sintered alloy body includes a resin film layer andpores, the pores defining a porosity ranging from 2 to 35 volume %, eachhaving an inlet portion and an inside portion, thus defining a poreinlet diameter and a pore inside diameter,

[0018] wherein the pore inlet diameter ranges from 10 to 200 μm, and anaverage ratio of the pore inlet diameter to the pore inside diameter isat least 2.0.

[0019] Accordingly, the resin film layer enters into the pores andcontacts them so closely that the pores on the surface are sealed.

[0020] A sintered alloy according to a second aspect of the invention isthe one set forth in the first aspect, wherein the sintered alloy bodyis a bearing body.

[0021] Accordingly, the resin film layer is provided integrally on thebearing body, and seals the pores thereon, thus improving slidingproperties thereof.

[0022] A sintered alloy according to a third aspect of the invention isthe one set forth in the second aspect, wherein the resin film layer isprovided on at least one of end faces of the bearing body, the end facesbeing provided on axially opposite ends of the bearing body.

[0023] Thus, as the resin film layer serves as a washer member, therelative rotation between the bearing body made of sintered alloy andthe washer member made of resin film layer is suppressed, ratherresulting to the sliding between the washer member and the otherwashers, or to the sliding between the washer member and a snap ring,thus ensuring the preventing of the abrasion of the washer member due tothe sliding relative to the bearing body. Moreover, as the pores on theend face of the bearing body can be sealed by the washer member, the oilleakage from the end face of the bearing can be prevented effectively.

[0024] A sintered alloy according to a fourth aspect of the invention isthe one set forth in any of the foregoing aspects, wherein solidlubricant is dispersed in the resin film layer.

[0025] Thus, as there is provided the resin film layer in which thesolid lubricant is dispersed, the coefficient of friction can be simplyreduced. Further, as the resin coating is applied in the form ofadhesion matrix, the washer member can contain comparatively a lot ofsolid lubricant therein.

[0026] A sintered alloy according to a fifth aspect of the invention isthe one set forth in the fourth aspects, wherein the solid lubricantmakes up 1 to 40 volume % of the resin film layer, as it is difficult toobtain friction-reducing effect with the solid lubricant less than 1volume %, while the strength of the resin film layer is lowered with thesolid lubricant more than 40 volume %. Accordingly, it is possible toobtain the friction-reducing effect without lowering the strength of theresin film layer by employing the range proposed in this aspect.

[0027] A method of manufacturing a sintered alloy according to a sixthaspect of the invention is the one for manufacturing the sintered alloyset forth in the first aspect, comprising the step of forming the resinfilm layer on the sintered alloy body, using solid lubricant coating.

[0028] Although the sintered alloy body has normally a large frictionalresistance due to the presence of pores on the surface, the frictionalresistance can be simply reduced by providing the resin film layercontaining the solid lubricant. Also, the resin film layer enters intothe pores and contacts them so closely that the pores are sealed.

[0029] A method of manufacturing a sintered alloy according to a seventhaspect of the invention is the one set forth in the sixth aspect,wherein the sintered alloy body is a bearing body.

[0030] Accordingly, the resin film layer is provided integrally on thebearing body, and seals the pores thereon, thus improving sidingproperties thereof.

[0031] A method of manufacturing a sintered alloy according to an eighthaspect of the invention is the one set forth in the seventh aspect,wherein the resin film layer is provided on at least one of end faces ofthe bearing body, the end faces being provided on axially opposite endsof said bearing body.

[0032] Thus, as the resin film layer integrated with the bearing bodyserves as a washer member, the relative rotation between the bearingbody made of sintered alloy and the washer member made of resin filmlayer is suppressed, rather resulting to the sliding between the washermember and the other washers, or to the sliding between the washermember and a snap ring, thus ensuring the preventing of the abrasion ofthe washer member due to the sliding relative to the bearing body.Moreover, as the pores on the end face of the bearing body can be sealedby the washer member, the oil leakage from the end face of the bearingcan be prevented effectively.

[0033] A method of manufacturing a sintered alloy according to a ninthaspect of the invention is the one set forth in any one of the sixth toeight aspects, wherein the resin film layer is pressed against thesintered alloy body after forming the resin film layer.

[0034] Accordingly, the pressing of the resin film layer facilitates theresin film layer to enter into the pores of a porous body, thusimproving the tightness therebetween, while smoothing the surface,eliminating the need for preliminary leveling process.

[0035] A method of manufacturing a sintered alloy according to a tenthaspect of the invention is the one set forth in the ninth aspect,wherein the pressing is performed by a sizing process.

[0036] Accordingly, the pressing process is performed simultaneouslywith the sizing of the sintered alloy body, thus realizing thetight-fitness of the resin film layer as well as the smoothing of thesurface.

[0037] A method of manufacturing a sintered alloy according to aneleventh aspect of the invention is the one set forth in any one of thesixth to eight aspects, wherein the resin film layer is formed by aprinting process of the solid lubricant coating.

[0038] Accordingly, the printing process allows the resin film layer toenter into the pores and closely contacts them, thus sealing the poreson the surface.

[0039] A method of manufacturing a sintered alloy according to a twelfthaspect of the invention is the one set forth in the eleventh aspect,wherein the printing process is a screen printing process.

[0040] Thus, as the resin film layer is provided by screen printingprocess, even a comparatively thick resin film layer can be formedeasily by the screen printing as compared with conventional process suchas spray coating process. Further, by the screen printing process, theresin film layer can be formed to a desirable pattern more simply thanby other processes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] For more complete understanding of the present invention,reference is now made to the following description taken in conjunctionwith the accompanying drawing, in which:

[0042]FIG. 1 is cross-sectional view illustrating a screen printing inaccordance with a first embodiment of the invention.

[0043]FIG. 2 is a cross-sectional view illustrating a step of pressing aresin film layer to a sliding surface in accordance with the firstembodiment of the invention.

[0044]FIG. 3 is a micro photographic view showing a sintered alloy bodyprior to a sizing process in accordance with an embodiment of theinvention.

[0045]FIG. 4 is a flow chart showing a manufacturing method inaccordance with another embodiment of the invention.

[0046]FIG. 5 is a cross-section of a sliding member in accordance withthe second embodiment of the invention.

[0047]FIG. 6 is a cross-section illustrating a tissue at an end face ofthe sliding member in accordance with an embodiment of the invention.

[0048]FIG. 7 is a cross-sectional view illustrating a sizing process inaccordance with an embodiment of the invention.

[0049]FIG. 8 is an explanatory diagram showing a surface roughness of aresin film layer, in which FIG. 8(A) shows the same before the sizingprocess, while FIG. 8(B) the same after the sizing process.

[0050]FIG. 9 is a plan view showing a sliding member in accordance withan embodiment of the invention.

[0051]FIG. 10 is a cross-sectional view illustrating the sliding memberin accordance with an embodiment of the invention.

[0052]FIG. 11 is an explanatory cross-sectional view illustrating ascreen printing in accordance with an embodiment of the invention.

[0053]FIG. 12 is a partly enlarged cross-sectional view showing asliding member in accordance with an embodiment of the invention.

[0054]FIG. 13 is a flow chart showing a manufacturing method inaccordance with an embodiment of the invention.

[0055]FIG. 14 is a cross-section of a shaft and a sintered bearing inaccordance with an embodiment of the invention.

[0056]FIG. 15 is a cross-sectional view illustrating a tissue at aboundary surface between a bearing body and a resin film layer inaccordance with an embodiment of the invention.

[0057]FIG. 16 is a cross-sectional view illustrating a screen printingin accordance with an embodiment of the invention.

[0058]FIG. 17 is a cross-section of a shaft and a sintered bearing inaccordance with an embodiment of the invention.

[0059]FIG. 18 is a cross-section of a shaft and a sintered bearing inaccordance with an embodiment of the invention.

[0060]FIG. 19 is a cross-section of a shaft and a sintered bearing inaccordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0061] Hereunder is a description of embodiments of the presentinvention with reference to the attached drawings.

[0062] In FIGS. 1-3 showing an embodiment of the invention, referencenumeral 1 designates a sintered alloy body whose porosity is in a rangeof from 2 to 35 volume % in this embodiment. The sintered alloy body 1is a sliding member having a sliding surface 2, which is formed with aresin film layer 3 as a printed layer, using solid lubricant coating 110or the like. The resin film layer 3 thus formed is pressed against thesliding surface 2 to thereby bring the resin film layer 3 into closecontact with the sliding surface 2.

[0063] The aforesaid sintered alloy body 1 has pores each having adiameter of 10 to 200 μm (preferably of 20 to 100 μm) at its inlet side(hereinafter called “pore inlet diameter), and that an average ratio ofthe “pore inlet diameter” to a “pore inside diameter” is at least 2.0 inthe said pore (preferably in a range from 2 to 20, more preferably from5 to 20). As above described, porosity here is in the range of 2-35volume % (preferably 10 to 25 volume %).

[0064] The aforesaid sintered alloy 1 is obtained by mixing materialpowders mainly composed of metal in a preset mixing ratio, performing ablending process for well blending the material powders, and thenforming the same into a green compact of a predetermined configurationby applying a preset pressure thereto, and then sintering the greencompact.

[0065] For the resin coating which forms the resin film layer 3 may beused the coating of solid lubricant coating. Coating methods thereof maybe for example a tumbler method in which an object to be coated is putin a tumbler, and then solid lubricant coating is sprayed to the objectwhile being stirred by circulating or vibrating the tumbler; a spraymethod in which solid lubricant coating is sprayed from a spray gun tothe object; and a dipping method in which the object is dipped in solidlubricant coating. Further, when the solid lubricant coating is appliedto a limited predetermined section on a surface of the object, a maskingtape or the like may be attached to a portion to which no coating is tobe applied, and then spray coating is applied, and the masking materialis removed thereafter.

[0066] The solid lubricant coating 110 for use with printing maybeproduced by dispersing a large amount of fine particles of solidlubricant in binder solution, said binder solution being obtained bysolving binder resin in solvent. For such binder resin may be usedpolyamide-imide resin, epoxy resin, furan resin, melamine resin, acrylicresin, urethane resin or the like. Taking adhesion and mechanicalstrength into consideration, however, it is desirable to usetwo-component system epoxy of amine hardening type. For solvent may beemployed xylene, toluene, butanol, isobutylalcohol, isopropylalcohol,dioxane, methyl ethyl ketone, N-methyl-2-pyrrolidone or the like. Forsolid lubricant may be employed PTFE (polytetrafluoroethylene, i.e.,“Teflon” (registered trademark), PFA(polytetrafluoroethylene-perfluoroalkylvinylether copolymer, i.e.,“Teflon” (registered trademark), C (graphite), MoS₂ (molybdenumdisulfide), BN (boron nitride), WF (tungsten fluoride), and TiN(titanium nitride) or the like, which may be used alone or in a mixturethereof. To the solid lubricant coating may be added dispersant,antifoamer, stabilizer, fire retardant, hardening accelerator, pigmentsand the like.

[0067] Silkscreen printing is one of desirable printing methods.Silkscreen printing is a kind of stencil printing. As illustrated inFIG. 1, meshed silk, nylon, Tetron, or stainless steel is put on a frame111 to thereby provide a screen 112, which is formed with a patternformation layer 113 forming a part that the solid lubricant coating 110or ink passes through and a part that it does not, so that the ink onthe screen 112 is pushed out with a squeegee 114 so as to print adesirable figure on the surface of an object.

[0068] In some embodiments, printing is performed with a 3-6 mmclearance between the said screen 112 and the surface of the object.Silkscreen printing is advantageous in that plate making is easy andinexpensive, and a printing machine therefor has a simple structure andis easy to use. Particularly in the case that ink is the solid lubricantcoating 110, solid lubricant fine particles of large specific gravity isprevented from being separated due to the solid lubricant coating 110supplied on the screen 112 being always stirred by the squeegee 114, andthus there is an advantage that the resin film layer 3 of high qualityis able to be obtained. Moreover, silkscreen printing is suitable forprinting a flat surface such as the end face 11A.

[0069] In the meantime, printing methods of the invention should not belimited to the silkscreen printing, but other printing method such aspad printing, for example, may be used. In the pad printing, the resinfilm layer 3 can be printed by pressing a transcriptional pad against anobjected to be printed after the transcriptional pad is pressed againsta printing plate coated with the solid lubricant coating 110 to attachthe ink prescribing a predetermined pattern thereto. In the event thatthe printing of the solid lubricant coating 110 is performed by otherprinting methods than the silkscreen printing, it is desirable toprovide a stirring device in an ink reservoir of the printing machine,and to always stir the solid lubricant coating 110 during printing inorder to prevent the solid lubricant from being separated. The resinfilm layer 3 thus formed has the aforesaid solid lubricant dispersed ina proportion of 1-40 volume %.

[0070] According to the foregoing silkscreen printing method, it ispossible to determine the thickness of a printing layer of the solidlubricant coating 110 depending on the thickness of the patternformation layer 113. For example, with the printing layer of 200 μmthickness, dry thickness after baking processing at about 80 degreescentigrade becomes about 60-70 μm.

[0071] One of preferred examples of the lubricant coating 110 is amixture of 100 parts by weight of screen process ink for metal coating(product name: “SS25-000” by Toyo Ink Seizo K.K., epoxy resin) andpreferably 10 to 30 parts by weight of PTFE having an average particlediameter 20-50, μm to which is further added preferably 5 to 20 parts byweight of exclusive solvent to obtain a suitable viscosity for printing,thus obtaining the ink for screen printing.

[0072] In the printing layer, the solid lubricant having small surfaceenergy is exposed to the surface side thereof, thus increasing thedensity of the solid lubricant on the surface side of the resin filmlayer 3, displaying an excellent sliding characteristic.

[0073] It is preferable to fully degrease the surface of the sinteredalloy body 1 prior to the printing of the solid lubricant coating 110 soas to perform preliminary surface adjustment. In the event that thesintered alloy body 1 is an iron-based one, blast processing or the likemay be performed as such surface adjustment. It is also preferable topreheat the sintered alloy body 1 at the time of the printing of thesolid lubricant coating 110 in order to remove moisture from the surfaceof the sintered alloy body 1 and to improve the durability of the resinfilm layer 3. Although, the resin film layer 3 is subjected to bakingprocess after the printing of the solid lubricant coating 110, it ispreferable to dry the resin film layer 3 temporarily prior to the bakingprocess in order to protect the resin film layer 3 during thetransportation to a heating furnace.

[0074] The solid lubricant coating 110, includes a large amount of thesolid lubricant fine particles dispersed in the binder solution, isapplied by screen printing process, it is possible to perform printingprocess more easily and at lower costs, as compared with the coating byspray gun, preventing the dispersion of the coating while reducing theloss of coating, thus preventing the solid lubricant coating fromadhering to unnecessary portions.

[0075]FIG. 3 is a microgram (495×) of the sintered alloy body 1 prior tosizing process. Preferred solid lubricant coating is ink for use withmetal coating, such as “SS25-000” (epoxy resin) and/or “SS16-000”(urethane resin) made by Toyo Ink Seizo K.K. PTFE is dispersed in them,and the resin film layer 3 thus obtained includes about 30 volume % ofPTFE in a dispersed state. It is understood that the resin film layer 3enters into the pores, in close contact therewith, while the surface ofthe resin film layer 3 is comparatively flat even before sizing process.

[0076] After the resin film layer 3 is provided integrally with thesintered alloy body 1 in the above-mentioned manner, the resin filmlayer 3 is pressed against the sliding surface 2 of the sintered alloybody 1. For instance, the resin film layer 3 may be pressed against thesliding surface 2 by a pressing means 4 which abuts to the surface ofthe resin film layer 3 and presses the same toward the sliding surface2, as illustrated in FIG. 2, so that the resin film layer 3 enters thepores on the sliding surface 2 to be brought in close contact therewith,thus eliminating or relieving the need for surface preparation of thesliding surface 2 such as chemical surface treatment thereof prior tothe formation of the resin film layer 3 by printing.

[0077] In the meantime, it is desirable that the thickness T of the saidresin film layer 3 is 0.1 mm or more.

[0078] In FIGS. 4 to 7 showing a second embodiment of the invention, thesame portions as those described in the foregoing embodiment will bedesignated by the same reference numerals, and their repeated detaileddescription will be omitted. Meantime, the omission of repeated detaileddescriptions will apply to any of hereinafter-described third or laterembodiments as well.

[0079] After a raw material powder mainly composed of metal is mixed ina preset mixing ratio and the resultant mixture is subjected to blendingprocess (S1: step 1), it is formed into a green compact of a presetshape by applying a preset pressure thereto, using a press (S2). Then,the green compact is subjected to sintering process (S3) to form theaforesaid sintered alloy body or a bearing body 11. Then, the solidlubricant coating 110 is applied to one end face 11A of the bearing body(S4) to form the resin film layer 3. The bearing body 11 formed with theresin film layer 3 thus way is subjected to sizing process (S5) as are-compression process, and then finished to a preset size. By thissizing process (S5), the resin film layer 3 is pressed against the endface 11A serving as a sliding surface. Incidentally, for saidapplication of coating (S4) is preferably used a printing method.

[0080] The bearing body 11 is a cylindrical sintered body obtained bysintering a green compact formed by compacting metallic raw materialpowders such as iron and copper. The bearing body 11 is a sliding memberincluding a through-hole 12 in the center thereof, rotatably supportingan axial body 13 serving as a rotating element on an inner peripheralsurface of the through-hole 12. Numeral 14 is a ring integrally fixed tothe axial body 13, said ring 14 regulating the thrust movement of theaxial body 13 by contacting the resin film layer 3 formed on the endface 11A of the bearing body 11. As above described, the bearing body 11is a sintered body obtained by sintering a green compact formed bycompacting metallic raw material powders such as iron and copper, whichis so-called oil-retaining bearing which impregnates the sintered bodywith oil.

[0081] As for the surface of the end face 11A of the bearing body 11,the bearing body 11 has a pore 101 having an inlet diameter Φs in arange of 10 to 200 μm (preferably 20 to 100 Em), like the firstembodiment, as shown FIG. 6, and that an average ratio of the “poreinlet diameter Φs” to a “pore inside diameter (Di” is at least 2.0 inthe said pore 101 (preferably in a range from 2 to 20, more preferablyfrom 5 to 20). As above described, porosity here is in the range of 2-35volume % (preferably 10 to 25 volume %).

[0082] As there exist a lot of pores 101 (open pores) as above, theresin film layer 3 is allowed to enter these open pores 101, thusrigidly fixing the resin film layer 3 to the bearing body 11. Further,as the pores 101 which are open on the end face 11A of the bearing body11 are sealed by the resin film layer 3, the lubricant leakage therefromis controlled. Moreover, coating is applied to the surface of thebearing body by printing or the like, without applying any chemicaltreatment thereto, yet the solid lubricant coating 110 enters fineirregularities 102 on the surface of the end face 11A. Specifically, thesizing process facilitates the resin film layer 3 to enter into the openpores 101 and irregularities 102, thus improving the tightnesstherebetween.

[0083]FIG. 7 shows a sizing die assembly 21 used for sizing process. Thesizing die assembly 21 assumes that the vertical direction is its axialdirection (pressing longitudinal direction), including a die 22, a corerod 23, a lower punch 24 and an upper punch 25. The die 22 issubstantially cylindrical, with the column-shaped core rod 23 beingpositioned coaxially therewith.

[0084] The lower punch 24 is also formed substantially cylindrical,fitting in between the die 22 and the core rod 23 from a lower side, ina manner capable of moving up and down freely so that it may be taken inor out from there freely. The upper punch 25 is also formedsubstantially cylindrical, fitting in between the die 22 and the corerod 23 from an upper side, in a manner capable of moving up and downfreely so that it may be taken in or out from there freely. As shown inFIG. 7, the bearing body 11 is placed inside the die 22 with the corerod 23 being positioned in the through-hole 12 serving as a slidingsurface of the bearing body 11. Then, the bearing body 11 is pressedfrom the upper and lower directions, using the upper and lower punches25 and 24 so that the bearing body 11 is corrected to take a propersize. Due to the pressure applied at that moment, the resin film layer 3is pressed against the end face 11A serving as a sliding surface.

[0085]FIG. 8 illustrates surface roughness of the resin film layer 3.For the resin film layer 3 is used the solid lubricant coatingcomprising a blend of 100 parts by weight of screen process ink (productname: “SS25-000” by Toyo Ink Seizo K.K.) and 30 parts by weight of PTFEhaving an average particle diameter 50 pm. The solid lubricant coatingwas printed on the said end face 11A so that the resin film layer 3 wasformed. Also, in the sizing process, pressure was applied for two orthree seconds, at 100-300 MPa, so that the resin film layer 3 waspressed against the end face 11A.

[0086] It is understood that FIG. 8(A) shows the surface roughness ofthe resin film layer 3 before the sizing process, while FIG. 8(B) showsthat after the sizing process, and that the irregularities of the resinfilm layer 3 were reduced and thus the layer 3 was smoothed.

[0087] As the resin film layer 3 is provided on the end face 11, and theresin film layer 3 is pressed by pressing forces applied by the upperand lower punches 24, 25, orthogonally relative to the end face 11A, sothat the tightness between the resin film layer 3 and the end face 11Ais ensured, enabling the smoothing of the resin film layer 3simultaneously.

[0088] FIGS. 9-11 show another embodiment of the invention, in which therepeated detailed descriptions of the same portions will be omitted likethe foregoing embodiments.

[0089] In the present embodiment showing the bearing body 11, asillustrated in FIG. 9, two or more dynamic pressure generating grooves 5are arranged equidistantly along circumferential directions between arcportions 3A of the resin film layer 3. It should be noted that thedynamic pressure generation grooves 5 are defined by not providing theresin film layer 3, thus forming the dynamic pressure generation grooves5 each having a depth corresponding to the thickness T of the resin filmlayer 3. The end face 11A is exposed to the external in the dynamicpressure grooves 5, while the dynamic pressure generation grooves 5 aretapered toward the center, such that the arc portions 3A of the resinfilm layer 3 and the dynamic pressure generation grooves 5 are arrangedalternately in a manner like a vortex as a whole. In that case, it iseasy to form the dynamic pressure generation grooves 5, using silkscreenprinting, by matching the pattern formation layer 113 to the pattern ofthe resin film layer 3 as shown in FIG. 11.

[0090] The lubricant included in the pores of the bearing body 11 oozesin association with the rotation of the axial body 13 which axiallysupports the bearing body 11, thus forming an oil film between theperipheral inner surface (which serves as a sliding surface) of thethrough-hole 12 of the bearing body 11 and the peripheral outer surfaceof the axial body 13 as well as between the end face 11A of the bearingbody 11 and the ring 14 fixed integrally to the axial body 13. The oozedlubricant is, in association with the rotation of the axial body 13,flows in the rotational direction of the axial body 13, along thedynamic pressure generation grooves 5 formed on the end face 11A on oneside of the bearing body 11 sliding relative to the ring 14, thusproducing pressure, generating dynamic pressure, i.e., oil pressure inthe direction supporting the axial body 13.

[0091] As is apparent from the foregoing, whilst the lubricant includedin the pores of the bearing body 11 oozes in association with therotation of the axial body 13, a portion of the end face 11A which iscovered with the resin film layer 3 is prevented from the lubricant'sleakage, and the leakage of the lubricant only occurs in the dynamicpressure generation grooves 5 formed in the resin film layer 3. Further,as the ring 14 which regulates the thrust movement of the axial body 13does not come into direct contact with the bearing body 11 but intocontact with the resin film layer 3, the abrasion of the end face 11A ofthe bearing body 11, said end face 11A serving as a sliding surfacerelative to the ring 14, is suppressed, thus eventually preventing theabrasion of the dynamic pressure generation grooves 5 since the dynamicpressure generation grooves 5 are formed by the resin film layer 3. As aresult, a high dynamic pressure can be maintained in the dynamicpressure generation grooves 5. Moreover, as the resin film layer 3 whichforms the dynamic pressure generation grooves 5 is formed on the bearingbody 11 by the coating process such as printing, dynamic pressuregeneration grooves 5 can be formed extremely easily as compared withconventional methods such as cutting using a NC lathe and rolling.Additionally, compacting accuracy of the dynamic pressure generationgrooves 5 improves, thus realizing an excellent dynamic pressurecharacteristic. Practically, the resin film layer 3 of a desirable shapecan be formed, by using a screen process printing.

[0092] The present embodiment is particularly advantageous, in additionto the above-mentioned advantages of the foregoing embodiments, in thatthe formation process of the dynamic pressure generation grooves 5 issimply performed, as the bearing body 11 is formed with the resin filmlayer 3 by printing process, while forming the dynamic pressuregeneration grooves 5 by providing blanks in printing.

[0093] In FIG. 12 showing a fourth embodiment of the invention, theresin film layer 3 is formed in the through-hole 12 (serving as thesliding surface) of the bearing body 11 by the coating process such asprinting. Therefore, the friction between the through-hole 12 and theaxial body 13 can be reduced due to the resin film layer 3 in which thesolid lubricant is dispersed.

[0094] As the resin film layer 3 is provided in the through-hole 12 inthe bearing body 11 of which the porosity is 2-35%, the friction betweenthe axial body 13 and the through-hole 12 as a sliding surface can bereduced, thus attaining the same effect and action as the foregoingembodiments.

[0095] In FIGS. 13-16 showing a fifth embodiment of the invention, thesintered bearing 10 of this embodiment includes the bearing body 11formed by sintering a green compact obtained by compacting materialpowders, and the resin film layer 3 formed integrally with the end face11A of the bearing body 11 by resin coating process, in which said resinfilm layer 3 serves as a washer member 14 in this embodiment. Thesintered bearing 10 supports the shaft S rotatably, retaining lubricantin the bearing body 11 composed of the sintered alloy body, enabling thelubricant to ooze from a peripheral inner surface 11B by rotating theshaft S. The shaft S is subjected to a thrust load in the directionindicated by an arrow as shown in FIG. 14, while a snap ring R ispress-fitted through the shaft S and abuts to the sintered bearing 10through two or more washers WA, WB, WC, thus regulating thrust movementthereof. In the meantime, this sintered bearing 10 is a so-called ballbearing, which is capable of automatic core-adjustment as a side surface11C is formed spherical.

[0096] The bearing body 11 is a cylindrical sintered body obtained bycompacting metallic material powders such as iron and copper, and thensintering a green compact thus molded, As there exist a lot of pores(open pores) on the end face 11A of the bearing body 11, as shown inFIG. 15, the resin film layer 3 is allowed to enter these open pores,thus rigidly fixing the washer 14 (made of the resin film layer 3) tothe bearing body 11. Further, as the pores which are open on the endface 11A of the bearing body 11 are sealed by the washer 14, thelubricant leakage therefrom is controlled.

[0097] For resin coating which makes up the washer member 14 may beemployed a mixture of certain resin having adhesion properties, used asadhesion matrix, and certain solid lubricant. For the solid lubricantmay be used the one which improves the lubricating properties of thewasher member made of the resin film layer 3. For example, PTFE(“Teflon” (registered trademark), C (graphite), MoS₂ (molybdenumdisulfide), BN (boron nitride), WF (tungsten fluoride), and TiN(titanium nitride) or the like may be used, which may be used alone orin a mixture thereof. In the meantime, the solid lubricant of theinvention includes hard particles for imparting lubricating properties,such as sericite. Alternatively, resin that has lubricating propertiesitself may be applied to form the washer member 14, without mixing thesolid lubricant. Whilst coating is employed to form the resin film layer3, various methods may be employed as long as they are able to form theresin film layer 3 on the end face 11A. Incidentally, the thickness T ofthe washer member 14 is desirably 0.1 mm or more.

[0098] The thickness T is defined by the distance between the end face11A and the outer surface of the washer member 14. The washer member 14has an inside diameter which is larger than the outside diameter of theshaft S (i.e., loose fit) so that the peripheral inner surface 12A maynot slide on the peripheral surface of the shaft S, while the outsidediameter of the washer member 14 is formed as large as possible. Thatis, as the washer member 14 is so formed that the peripheral innersurface 12A does not contact the peripheral surface of the shaft S, itis not subjected to any force developed in the rotational direction ofthe shaft S. Also, as the outside diameter of the washer member 14 isformed larger than the washer WC contacting the washer member 14directly, the abrasion of the washer WC due to contacting and sliding onthe end face 11A of the bearing body 11 is prevented.

[0099] After forming the washer member 14 made of the resin film layer 3integrally on the bearing body 11 in this way, the sizing process isperformed so as to allow the sintered bearing 10 to take a properpredetermined size, and then oil is supplied to the bearing body 11 toimpregnate it with oil.

[0100] In the meantime, the washer WA is pressed into the shaft S, andthe snap ring R and the washer WA are rotated integrally, while thewashers WB and WC are loose-fitted to the shaft S, whereby it ispossible to limit sliding surfaces only to contact surfaces betweenadjacent resins, such as a contact surface between the washer WA and thewasher WB, or a contact surface between the washer WC and the washermember 14, whereby the sliding between the washer WA and the snap ring Ris suppressed, thus reducing the abrasion of the washer WA.

[0101] According to the present embodiment, as the washer member 14 madeof the resin film layer 3 is integrally provided on at least one of theend faces 11A of the bearing body 11, and thus the washer member 14 isintegrated with the bearing body 11, so that the relative rotationbetween the bearing body 11 made of sintered alloy and the washer member14 made of resin is suppressed, rather resulting to the sliding betweenthe washer member 14 and the other washers, or to the sliding betweenthe washer member 14 and the snap ring R, thus ensuring the preventingof the abrasion of the washer member 14 due to the sliding relative tothe bearing body 11. Moreover, as the washer member 14 can seal thepores on the end face 11A of the bearing body 11, the oil leakage fromthe end face 11A of the bearing can be prevented effectively.

[0102] As described above, as the washer member 14 includes the solidlubricant in this embodiment, the lubricating properties are improved.As the resin coating is applied in the form of adhesion matrix, thewasher member 14 can contain comparatively a lot of solid lubricanttherein.

[0103] Also, according to the present embodiment, there is provided amethod of manufacturing a sintered bearing, said sintered bearingincludes: the bearing body 11 formed by sintering a green compactobtained by compacting material powders; and the washer member 14 madeof the resin film layer 3, said washer member 14 being provided on atleast one of the end faces 11A of the bearing body 11, wherein saidwasher member 14 is formed by applying the resin thereto, said resinincluding the solid lubricant.

[0104] Accordingly, the washer member 14 is formed integrally with thebearing body 11, so that the relative rotation between the bearing body11 made of sintered alloy and the washer member 14 made of resin issuppressed, rather resulting to the sliding between the washer member 14and the other washers, or to the sliding between the washer member 14and the snap ring R, thus ensuring the preventing of the abrasion of thewasher member 14 due to the sliding relative to the bearing body 11.Moreover, as the washer member 14 can seal the pores on the end face 11Aof the bearing body 11, the oil leakage from the end face 11A of thebearing can be prevented effectively. In addition, owing to the solidlubricant included in the washer member 14, the lubricating propertiesthereof are improved, and that since the resin coating is applied in theform of adhesion matrix, comparatively a lot of solid lubricant can becontained in the washer member 14.

[0105] It is also noted that the present embodiment is advantageous inthat the sintered bearing 10 inclusive of the washer member 14 can befinished to a precise dimension, as the sizing process is performedafter providing the washer member 14 in the bearing body 11.

[0106] Referring to FIG. 17 showing a sixth embodiment of the invention,the washer member 14 is composed of two layers, i.e., the resin filmlayers 3 and 3′ provided on the end face 11A. Initially, the first layer(i.e., the resin film layer 3) is formed on the end face 11A, and thenthe second layer (i.e., the resin film layer 3′) is formed on the firstresin film layer 3. The thickness T′ of the washer member 14 can beformed thick by providing the resin film layers in such multi-layerformation. Moreover, a desired performance of the washer, such as goodlubricating properties, can be obtained by including lubricant at leastin the resin film layer 3′ that is exposed to the surface.

[0107] Referring to FIG. 18 showing another embodiment of the invention,a sintered bearing 30 of the embodiment is a self-aligning bearing ofwhich the surface contacting a housing H is formed substantiallyspherical. A washer member 32 is provided so as to cover a lower part ofa bearing body 31 (the sintered alloy body) from a lower end face 31A toa lower part of a side face 31D thereof. A washer member 33 is providedso as to cover an upper part of the bearing body 31 from an upper endface 31C to an upper part of the side face 31D thereof. These washermembers 32 ad 33 are provided integrally on the bearing body 31 by resincoating, and are pressingly held relative to the housing H by a springwasher WD.

[0108] The washer members 32 and 33 are each composed of a single layerof the resin film layer 3 or multiple layers thereof, like the foregoingwasher member 14. The washer members 32 and 33 are each fixed in such amanner that covers the bearing body 31 from the lower end face 31A tothe lower part of the side face 31D, and from the upper end face 31C tothe upper part of the side face 31D thereof, respectively, therebyforming opposite end faces 30C and 30A, and side faces 30B of thesintered bearing 30. Like the foregoing embodiments, the washer members32 and 33 are rigidly fixed to the bearing body 31 due to the resin in amolten state entering the open pores on the end face 31A of the bearingbody 31.

[0109] The sintered bearing 30 thus formed is held pressingly relativeto the housing H by the spring washer WD made of a metallic materialwhich has a spring characteristic such as copper sheet, so that it isself-aligned. According to the sintered bearing 30 of the presentembodiment, the spring washer WD is allowed to abut to the washer member33 made of the resin, which means that the one pressed against thehousing H is the washer member 32 made of the resin, thereby enablingthe reduction of the friction of the sintered bearing 30 relative to thehousing H and the spring washer WD, realizing the smooth self-aligningof the bearing.

[0110] It is to be noted herein that in this sintered bearing 30 showingin FIG. 18, the resin coating is not applied to a central part on theside 31D of the bearing body 31, and thus the sintered surface isexposed to the outside in an annular manner. This sintered surfaceserves as an oil-refilling surface 30B for supplying lubricant to thesintered bearing 30 (bearing body 31) from an oil refilling mechanism Fwhich is made of felt, for example, and disposed along the outerperiphery of the sintered bearing 30. In the event that the lubricantretained in the sintered bearing 30 decreases due for example to theconsumption thereof by the rotation of the shaft S or to the oilleakage, the lubricant can be supplied to the sintered bearing 30(bearing body 31) from the oil refilling mechanism F through the oilrefilling surface 30B where no resin is fixed.

[0111] Referring to FIG. 19 showing another embodiment of the invention,a sintered bearing 34 of the present embodiment does not provide the oilrefilling surface 30B described in the seventh embodiment, but forms thesingle or multi-layered resin film layers 3 in a manner covering bothend faces 35A, 35C and side surface 35B entirely. With such structure,it is possible to prevent the lubricant from oozing from both end faces35A, 35C and the side surface 35B of the bearing body 35 owing to awasher member 36, thus eliminating the need for the oil refillingmechanism, enabling the simplifying of the structure around the bearing.

[0112] It should be noted that the present invention should not belimited to the above-mentioned embodiments but various modifications arepossible within the scope of the invention. Resins and solid lubricantsshould not be limited to the described ones, but various kinds and typesthereof may be used. The sintered alloy of the invention may beapplicable to other various configurations As is apparent from theforegoing, the present invention provides a sintered alloy which enablesthe reducing of coefficient of friction and the sealing of pores on asurface thereof as well as a method of manufacturing the same. Theinvention is applicable to sliding components such as bearings and otherdevices.

What is claimed is:
 1. A sintered alloy comprising: a sintered alloybody formed by compacting material powders and then sintering the same,wherein said sintered alloy body has pores providing a porosity 2 to 35volume %, each pore having an inlet portion having a pore inlet diameterand an inside portion having a pore inside diameter, wherein said poreinlet diameter is from about 10 to about 200 μm, and an average ratio ofsaid pore inlet diameter to said pore inside diameter is at least about2.0, wherein said sintered alloy body has a resinfilm layer on at leasta portion of a surface thereof.
 2. A sintered alloy according to claim1, wherein said sintered alloy body is a bearing body.
 3. A sinteredalloy according to claim 2, wherein said bearing body has end faces onaxially opposite ends of said bearing body and said resin film layer islocated on at least a portion of one of the end faces.
 4. A sinteredalloy according to claim 1, wherein solid lubricant is dispersed in saidresin film layer.
 5. A sintered alloy according to claim 2, whereinsolid lubricant is dispersed in said resin film layer.
 6. A sinteredalloy according to claim 4, wherein said solid lubricant makes up 1 to40 volume % of said resin film layer.
 7. A sintered alloy according toclaim 5, wherein said solid lubricant makes up 1 to 40 volume % of saidresin film layer.
 8. A sintered alloy of claim 4, wherein said resinfilm layer contains an effective amount of solid lubricant.
 9. Asintered alloy of claim 5, wherein said resin film layer contains aneffective amount of solid lubricant.
 10. A method of manufacturing asintered alloy comprising: forming a sintered alloy body, having porestherein providing a porosity of about 2 to above 35 volume %, whereineach pore has an inlet portion having a pore inlet of about 0 to about200 μm, and an inside portion having a pore inside diameter; wherein anaverage ratio of said pore inlet diameter to said pore inside diameteris at least 2.0, and forming a resin film layer comprising solidlubricant coating on at least a portion of a surface of the sinteredalloy body, using solid lubricant coating.
 11. A method of manufacturinga sintered alloy according to claim 10, wherein said sintered alloy bodyis a bearing body.
 12. A method of manufacturing a sintered alloyaccording to claim 11, wherein said bearing body is formed with endfaces an axially opposite ends thereof, and said resin film layer isprovided on at least a portion of one of the end faces.
 13. A method ofmanufacturing a sintered alloy according to claim 10, further includingthe step of pressing said resin film layer against said sintered alloybody after forming the resin film layer.
 14. A method of manufacturing asintered alloy according to claim 11, further including the step ofpressing said resin film layer against said sintered alloy body afterforming the resin film layer.
 15. A method of manufacturing a sinteredalloy according to claim 12, further including the step of pressing saidresin film layer against said sintered alloy body after forming theresin film layer.
 16. A method of manufacturing a sintered alloyaccording to claim 13, wherein said pressing is performed during asizing process.
 17. A method of manufacturing a sintered alloy accordingto claim 14, wherein said pressing is performed during a sizing process.18. A method of manufacturing a sintered alloy according to claim 15,wherein said pressing is performed during a sizing process.
 19. A methodof manufacturing a sintered alloy according to claim 10, wherein saidresin film layer is formed by printing said solid lubricant coating. 20.A method of manufacturing a sintered alloy according to claim 11,wherein said resin film layer is formed by printing said solid lubricantcoating.
 21. A method of manufacturing a sintered alloy according toclaim 19, wherein said printing comprises is a screen printing process.22. A method of manufacturing a sintered alloy according to claim 20,wherein said printing comprises is a screen printing process.